The invention relates to a fluid friction clutch, especially for a cooling fan of a fluid-cooled internal combustion engine.
A fluid friction clutch for the cooling fan of a fluid-cooled internal combustion engine is known from Fed. German Publ. Spec. No. 3,103,064, of which the housing provided with fan blades is mounted rotatably on a drive shaft driven by the internal combustion engine. The housing contains a reservoir for shear fluid and a working chamber. A rotor held on the drive shaft is arranged in the working chamber and together with the working chamber defines at least one shear gap. A valve device temperature-dependently controls the cycling of shear fluid between the working chamber and the reservoir, so that the clutch may be engaged and disengagend temperature-dependently. A substantially elongated bimetallic element, which controls the valve through an axially displaceable pin, is secured on an axial end face of the housing, in a retaining fitting. In the region of the mutually opposite ends or short sides of the bimetallic element the retaining fitting has stop faces which fix the ends both in the circumferential direction of the housing and axially and radially of the axis of rotation. In the known clutch two tongues are provided with spacing from one another on each of the short sides of the bimetallic element, and engage in axial leg parts of the substantially U-shaped retaining fitting. Between the tongues the leg parts carry tabs which fix the bimetallic element in its longitudinal direction between them. The tab of one of the two leg parts is adjoined by an opening which is of such large dimensions that the entire cross-section of the bimetallic element can be inserted. For the fitting of the bimetallic element the latter is firstly introduced into this opening, whereafter the two tongues are inserted at the opposite end into the associated apertures of the other leg part of the retaining fitting. In this action the bimetallic element is shifted towards the other leg part until the two tongues on the first-mentioned end snap into the allocated apertures of the leg part. The bimetallic element is held by its own stress in the apertures of the leg part of the retaining fitting and bears in its middle region on the pin of the valve device.
It is further known to hold the bimetallic element in apertures of radially extending cooling fins of the clutch housing by inherent stress.
In known fluid friction clutches the bimetallic element is held exclusively by its own stress. For example in repair work the bimetallic element can unintentionally be disengaged from its retention, which leads to failure of the temperature control of the clutch.
It is the problem of the invention to improve a fluid friction clutch, especially for the cooling fan of a fluid cooled internal combustion engine, so that unintentional disengagement of the bimetallic element is reliably prevented in a constructionally simple manner.